So politics is not just showbusiness for ugly people but also for deeply, woefully, eye-wateringly unfunny people. The most telling aspect of David Cameron’s appearance on David Letterman’s show wasn’t his inability to name the composer of Rule, Britannia! or correctly to translate the phrase Magna Carta (it’s “Get Carter” in Latin, fact fans). It wasn’t even that the three million Americans who regularly tune in to watch Letterman were doubtless wondering why Princess Diana’s butler was on their screens again.

A group of 40 campaigners gathered outside the American embassy in London today to protest against the incarceration of a US Army private accused of leaking information to whistleblowing website WikiLeaks.